1. Technical Field
The present invention relates generally to document protection using digital watermarking techniques.
2. Background of the Related Art
Digital watermarking is a well-defined art. The following are representative patents that describe watermarking techniques in the context of document or image printing.
U.S. Pat. No. 6,970,259 describes a print management system that implements a policy to determine a protection level for a document to be printed. The document is printed using watermarks, glyphs, and digital signatures, which are appropriate to the level of protection determined by the policy. A set of printers are managed by a print management system. Each printer can provide a range of protection technologies. The policy determines the protection technologies for the document to be printed. The print management system routes the print job to a printer that can apply the appropriate protections and sets the appropriate parameters in the printer. Copy evidence that can establish that a document is a forgery and/or tracing information that identifies the custodian of the document and restrictions on copying of the document and use of the information in the document are included in the watermark that is printed on the document. A document can be verified as an original or established as a forgery by inspecting the copy evidence and/or tracing information in the watermark.
U.S. Pat. No. 5,488,664 describes a method and device for protecting visual information against unauthorized access and modification using a printed cryptographic watermark includes printing a first array of shapes on a first sheet of material to be protected and printing a second array of shapes on a second sheet of material, which is transparent so as to form a developer for developing a watermark encoded in a combination of the first and second arrays of shapes. The watermark is encoded by preparing each array using black and white pixels.
U.S. Pat. No. 6,389,151 describes a document validating system. Documents are produced by beginning with a template that defines the placements of elements on the document and the interrelationships between hidden and visual information on the document. The template specifies the placement of elements such as images, photographs, and text and it also specifies the interrelationship between information that is visually perceptible to a user of the document and information that is hidden by means of digital watermarks. Different hidden digital watermark data is included in multiple elements of the document. The watermarks in the different graphic elements of the document are correlated to each other and correlated to the visual material on the document. The system also includes a physical characteristic reader for automatically reading a physical characteristic of a person presenting the document and multiple hidden digital watermarks from different elements of said document, and a comparator for comparing the output of the physical characteristic reader with information stored in the hidden digital watermarks.
In addition, software applications such as Microsoft Word provide a document author with the capability of defining a watermark prior to creating a document, as well as defining how the watermark should be “applied” to a given document.
While these prior art techniques provide generally useful solutions, they require that the watermark to be created and the manner in which it is to be applied to be predetermined. They do not afford an authorized entity the ability to create a custom watermark in a centralized manner that can then be applied dynamically during a given rendering operation.
The present invention addresses this need in the art.